Excipients are inactive substances used alongside the active pharmaceutical ingredients (APIs) in drug formulations.
They play a vital role in the stability, efficacy, and safety of the final dosage form.
In liquid dosage forms, excipients can serve various functions, including solubilizing agents, preservatives, suspending agents, viscosity modifiers, emulsifying agents, and flavouring agents, among others.
Here's a classification and explanation of excipients based on their function in liquid dosage forms:
1. Solubilizing agents:
Help dissolve poorly soluble APIs to improve bioavailability.
Examples: Water, ethanol, propylene glycol, polysorbate 80, sodium lauryl sulfate.
2. Preservatives:
To prevent microbial contamination and extend the shelf life of liquid dosage forms, preservatives are added.
Examples of preservatives include benzalkonium chloride, methylparaben, propylparaben, and sodium benzoate.
3. Suspending agents:
In formulations where the API is not completely soluble, suspending agents help disperse the API uniformly, ensuring consistent dosing.
Examples include carboxymethyl cellulose, xanthan gum, and hydroxyethyl cellulose.
4. Viscosity modifiers:
These excipients adjust the viscosity of the liquid dosage form to improve the mouthfeel, stability, and ease of administration.
Examples of viscosity modifiers include cellulose derivatives (e.g., hydroxypropyl methylcellulose), polyvinylpyrrolidone, and polyvinyl alcohol.
5. Emulsifying agents:
These are used in emulsion formulations to stabilize the mixture of two immiscible liquids (e.g., oil and water).
They work by reducing the surface tension between the two phases, allowing them to stay mixed.
Examples include lecithin, glyceryl monostearate, and sorbitan esters.
6. Flavouring agents:
Improve palatability, especially for pediatric formulations.
Examples: Fruit extracts, vanillin, ethylvanillin.
7. Sweetening agents:
Mask bitter taste to enhance patient compliance.
Examples: Sucrose, glucose, aspartame, saccharin, sucralose.
8. Colouring agents:
Add visual appeal and indicate strength or flavour.
Examples: FD&C dyes, iron oxide pigments.
9. Antioxidants:
Protect the formulation from oxidative degradation.
Examples: BHA, BHT, ascorbic acid.
10. Chelating agents:
Sequester metal ions to prevent formulation degradation.
Examples: Disodium EDTA, citric acid.